Subterranean drilling process



Sept. 3, 1963 E. HILL-BURN SUBTERRANEAN DRILLING PROCESS Filed Sept. 18. 1961 FIG. 2

FIG.

INVENTOR. EDWARD HlLLBlURN a {2mm ATTORNEY United States Patent 3,102,599 SUBTERRANEAN DRILLING PROCESS Edward Hillbum, New Orleans, La., assignor to Continental Oil Company, Ponca City, Okla., a corporation of Delaware Filed Sept. 18, 1961, Ser. No. 138,906 2 Claims. (Cl. 175-72) This invention relates to the art of drilling oil and gas well boreholes. More particularly, the present invention concerns a method for sealing thief or lost zones encountered in penetrating unusually porous or creviced earth formations whereby circulation of drilling fluid can be readily and substantially completely restored.

My invention has particular applicability in the drilling of oil or gas wells by the rotary method. In such a method, drilling is performed by rotating a bit attached to the end of a hollow drill pipe which extends downwardly through the well bore. As the drill pipe is rotated from'the surface, the bit cuts or grinds away the encountered formations into small fragments known as cuttings which must be removed from the hole in order that the drilling may satisfactorily progress. To effect the removal of these cuttings, a fluid commonly referred to as a drilling mud is continuously pumped down the drill pipe, through channels or openings located in the extremity thereof and more usually in the drill bit itself, and thence up through the annular spacing between the drill pipe and the wall of the borehole to the surface of the earth. The drilling fluid conveys the cuttings produced by the drill bit .to the surface of the earth, serves as a lubricant for the drill bit and in addition accomplishes other desirable objectives. One of the most important of such other functions is that of forming a more or less fluid-impervious filter cake coating adjacent to the wall of the borehole which in turn prevents or substantially retards fluid in the borehole from penetrating into and being wasted in the surrounding earth formations. Also, this coating prevents or efiectively minimizes flow of liquids such as brine from the strata into the borehole thereby obviating dilution and consequent objectionable alteration of the characteristics of the drilling fluid.

As can be inferred from the above brief description of the general characteristics of drilling fluids, these materials, particularly the more effective types, are fairly complex in composition and comparatively expensive. Consequently, the loss of drilling fluids into the various earths strata penetrated by the borehole such as forma tions containing an usually porous, loose, creviced or fractured area presents one of the most difficult problems encountered in drilling operations. As a matter of fact, wholesale loss in this manner can figure predominately in the total cost for drilling a well and in some cases even necessitate an abandonment of the particular operation.

In view of the severity of the problem involved, numerous expedients have been heretofore proposed for solving same. Generally, the first expedient to be tried consists of pumping so-called circulation restoring materials into the well. These restorers embrace a wide variety of materials which serve to collect in the fracture and bridge therein to eventually seal the fracture. Conventional circulation restorers include such materials as granular plastics, textile flock and fibers, mica, asbestos, ground nut shells, shredded. or ground-up tire carcasses and the like. The drawback of this method is that it only has particular usefulness in sealing fractures which do not exceed about Ar-inch in width.

In the event the foregoing expedient is-not applicable, a more drastic procedure is called for, such as the placement of a sealing plug that hardens or stiifens inside the fracture and adjacent to the well bore area containing 3,1fi2,599 Patented Sept. 3, 1963 the fracture. The time setting or cementitious material employed in the practice of plugging can suitably be a hydraulic inorganic cement or a resinous cement. The usual difiiculties encountered in the aforedescribed plugging treatment are the lack of control of the placing of the sealing material and oftentimes the substantial loss of cement experienced before proper setting and sealing has occurred.

In accordance with this invention there is provided a simple method for sealing lost circulation zones which is especially applicable in the event use of circulation restoring materials has failed to affect adequate sealing. Briefly stated, the method of this invention initially cornprises withdrawing the drill pipe and bit assembly upon encountering a lost zone and after drilling adjacently therebeyond. Upon withdrawal, there is snugly positioned about the drill bit and for the neighboring portion of the drill pipe, a bag fabricated from a liquid impervious membranaceous material. The drill bit is returned to drilling position and pumping of the drilling mud through the drill pipe is commenced. The mul inflates the bag forcing it against the formation face. Continued pumping forces the top of the bag away from the drill pipe and thus circulation is facilitated. Drilling is then commenced through the bottom of the bag and the differential of pressure existing between the lost circulation zone and the well bore maintains the bag sealed in place to the wall of the hole.

Further details illustrating this method can be noted by referring to the accompanying drawing wherein:

FIGURE 1 is a cross-sectional elevational view of the drill pipe-bit assembly specifically illustrating a manner of attaching a membranaceous bag to said assembly in accordance with this invention; and

FIGURE 2 illustrates the position of the inflatable bag shown in FIGURE 1 after circulation of the drilling fluid has been regained and prior to further drilling.

Referring specifically to FIGURE 1, a hollow drill pipe is shown at 10 disposed within a well borehole 11 which borehole penetrates an area of lost circulation at 12. The drill bit 13 is attached to the extremity of drill pipe 10 and the latter together with a portion of the drill pipe extending upwardly from the top-most extremity of the zone 12 is encompassed with a substantially liquid impervious bag member 14. In the particular embodiment shown, the top of the bag is sealingly attached to the drill pipe 10 by means of a suitable clamp shown at 15 in the drawing. This clamp may be a metallic spring clamp or may simply comprise strong rubber bands. Additionally, while not shown in the drawing, it is desirable to place a plurality of stretchable rubber bands or expandable metal clamps along the whole length of the bag so that in a noninflatable position the bag adheres relatively close to the periphery of the drill pipe. The

diameter of the bag is primarily dependent on the nature of the bag employed. For example, in utilizing a bag fabricated of relatively unyielding material, it is generally desirable to employ a diameter conforming essentially to or slightly larger than the diameter of the well at the lost zone. as for example rubber, more latitude as to undersizing can obviously be tolerated. It is to be noted that the bit rests on the bottom of the borehole which had been previously extended beyond the thief zone. The extent to which the drilling beyond the thief zone is accomplished depends principally on the width of the lost zone.

Generally, such an extension need not exceed about half the total width of the lost'zone. Correspondingly, it is desirable to have the top of the bag extend above the lost zone for a distance approximately equal to one half the total width of the lost zone. It warrants mentioning that Of course, where stretchable materials are used,

3 the necessary drilling contemplated for drilling beyond most lost zones can be accomplished by dry drilling.

The bag 14, as indicated previously, can be fabricated of any substantially liquid impervious material. For this purpose, canvas can be used or more preferably the bag can be fabricated of a plastic. The plastic may take the form of a film thereof or may be in the form of a woven fabric. As notable examples of clear self-sustaining plastic-films, which can be used for the purposes herein, there are polyethylene, polypropylene, the so-called super condensation polymers, and the like. Suitable plastic cloths from which the bag can be constructed include nylon and other strong synthetic fiber-based fabrics.

As indicated, FIGURE 2 illustrates the position the bag assumes once drilling mud is caused to be pumped through the drill pipe. The direction of flow of the drilling fluid is shown by the arrows in FIGURE 2. Thus, it can be seen that the drilling fluid progresses downwardly through the drill pipe and out from channels or holes contained in or near the vicinity of the drill bit and thence flows upwardly through the bag thereby forcing the top of the bag from the drill pipe. The drilling fluid then returns to the top of the well for recovery and subsequent reintroduction into the operation. As shown in FIGURE 2, the surface of the expander bag conforms to the surface of the area of lost circulation. This is accomplished by the differential of pressure existing between the interior of the well borehole and the lost circulation zone 12. This pressure difference will maintain the bag in a sealing position even though drilling is commenced through and beyond the lower extremity of encompassing bag.

When the well borehole is completed or any time prior thereto, a casing may be run through the bag and cemented. In such an operation, the positioned bag also serves to prevent loss of cement. If additional trips should be required before setting a casing, the hole size may be reduced from about A to /2-inch and a drillable guide run on the bit So as to facilitate insertion of the bit through the sealing member adjacent to the zone of lost circulation. This guide may be made of any soft drillable material such as plaster of Paris, etc.

As is evident from the above description, it is essential that the bag remain intact in the course of lowering the bit into the bottom of the well. Accordingly, it is oftentimes desirable, either because of the nature of the bag material used or the particular abrasive character of the various strata through which the bag is lowered, to protect the portion about the bit against rupture. Several ways may be employed to protect this susceptible portion Ki of the bag. One convenient way consists of encasing the portion of the bag about the bit with a highly abrasiveresistant d-rillable material such as a thin sheath of readily drillable metal, as for example, aluminum, magnesium, etc. Ordinarily, in the practice of my method, it is desirable to run a caliper survey in the borehole upon withdrawing the bit. With the information obtained in such a survey, a new bit size is preferably chosen having a diameter less than the minimum diameter noted for the borehole.

The above describes completely a preferred manner of carrying out the present invention. Variations of this particular mode as may readily appear to those skilled in the art are also contemplated. Accordingly, it is to be pointed out that the scope of the invention is not limited to any of the details enumerated hereinbelow except as these details are included as limitations within the appended claims.

I claim:

1. A method of drilling a well borehole penetrating a thief formation whereby drilling fluid circulation is maintained which comprises: withdrawing the drill bit after encountering a zone of lost circulation and drilling adjacently therebeyond; adherently positioning a bag substantially impervious to liquids about the drill bit, said bag having a length exceeding the width of the zone of lost circulation; returning the drill bit to drilling position; introducing drilling fluid through the drill bit thereby expanding and sealingly positioning the wall of the said bag aga-inst said lost circulation zone; and commencing drilling under substantially full fluid circulation condi tions.

2. A method in accordance with claim 1 wherein said substantially liquid impervious bag is a plastic bag.

References Cited in the file of this patent UNITED STATES PATENTS France Oct. 10, 1 960 

1. A METHOD OF DRILLING A WELL BOREHOLE PENETRATING A THIEF FORMATION WHEREBY DRILLING FLUID CIRCULATION IS MAINTAINED WHICH COMPRISES: WITHDRAWING THE DRILL BIT AFTER ENCOUNTERING A ZONE OF LOST CIRCULATION AND DRILLING ADJACENTLY THEREBEYOND; ADHERENTLY POSITIONING A BAG SUBSTANTIALLY IMPERVIOUS TO LIQUIDS ABOUT THE DRILL BIT, SAID BAG HAVING A LENGTH EXCEEDING THE WIDTH OF THE ZONE OF LOST CIRCULATION; RETURNING THE DRILL BIT TO DRILLING POSITION; INTRODUCING DRILLING FLUID THROUGH THE DRILL BIT THEREBY EXPANDING AND SEALINGLY POSITIONING THE WALL OF THE SAID BAG AGAINST SAID LOST CIRCULATION ZONE; AND COMMENCING DRILLING UNDER SUBSTANTIALLY FULL FLUID CIRCULATION CONDITIONS. 